Machining steels



Patented Oct. 30, 1945 2.388.214 momma STEELS Donald William Murphy,Bethlehem, Pa., assignor to Bethlehem Steel Company, a corporation ofPennsylvania Application August 27, 1941, aria] No. 408,493

No Drawing.s

2 Claims.

My invention relates to machining steels. My invention comprisesfree-machining or allied steels having a small percentage of boron. Italso comprises such steels containing other elements to givemachinability effects, such as sulphur, phosphorus or nitrogen.

I have discovered that boron in very small amounts in steel contributesmarkedly to its machinability. As is well known, there are definitelimits to the life of a cutting tool when used to machine steels, anddefinite limits to the speed at which the tool may be used. As the speedis increased, the life of the tool is shortened. I have found that when0.01% or even lesser amounts of boron are added to steels the life ofthe tool used thereon is greatly increased for a given speed, andconversely, for a particular tool life, the speed may be greatlyincreased.

I employ boron in amounts from 0.004% to 0.02%, usuall preferring to usein the neighborhood of 0.01%.

My invention is particularly eflicacious when both boron and sulphur areused in steels. Such steels possess machinability propertiesconsiderably in excess of those containing sulphur alone and, moreover,the presence of the boron in such steels overcomes to a considerabledegree certain disadvantages of sulphur in steel.

Sulphur, because of certain deleterious efiects, is normally kept low insteels, the sulphur content ordinarily running from about 0.02% to about0.04%. However, it is well known practice to make free-machining steelsby increasing the sulphur content so that the sulphur in open hearthsteels runs from about 0.07% to 0.20% and, in the case of Bessemersteels, from about 0.10% to 0.30%. These higher contents of sulphurrender such steels capable of being machined to give longer tool life(conversely. greater speeds with the same tool life), and the machinedsurface is orbetter character. The addition of these higher amounts ofsulphur, however, has the effect of producing a steel in which thesulphur tends to be more or less segregated. Furthermore, such steelsare more or less hot short depending upon the amount of sulphur present.

By including boron in such steels of higher sulphur content, I greatlyincrease the machinability characteristics and I overcome to aconsiderable degree some of the disadvantages of the higher sulphurcontents.

For example, a steel containing 0.15% sulphur possessed a cutting speedof 162 surface feet per minute for 100 minutes tool life. A steelcontaining the same sulphur content, namely, 0. 15%

sulphur, but also containing 0.01% boron, possessed a cutting speed of219 surface feet per minute for minutes tool life, an increase of about35%.

In addition to increasing the machinability of sulphur containingsteels, the boron greatly reduces the tendency of the sulphur tosegregate, thereby giving a much more uniform character to the steel.

I obtain substantial effects on sulphur-bearing steels as regardsmachinability and uniformity of product, by the use of various amountsof boron. The boron content may be varied from 0.004% to 0.015%, usingsulphur in amounts from 0.06% to 0.3%.

As indicated above, sulphur renders steels more or less hot short, thischaracteristic increas ng with increasing amounts of sulphur. Steels arefrequently needed possessing a high degree of machinability and, at thesame time, having a low order of hot shortness. But to obtain thenecessary machinability by means of sulphur it frequently happens thatsuch large amounts of this element are required as to be incompatiblewith- C Mn P 8 Si Per cent Per cent Per cent Per cent Per cent 2 ll 73077 304 .009 $3 l0 67 08 19 0i 4 20 .85 08 l3 05 (5 .20 85 015 .13 05 (6.20 86 016 l3 05 the boron content of these analyses varying between0.004% and 0.02%.

I have also found that boron and nitrogen cooperate very-efiectively insteels having free-cutting characteristlcs. Nitrogen by itself, whenused in suiilcient amount, gives good surface to machined steels andalso causes the steel to chip eflectively during the cutting operation.Nitrogen by itself, however, apparently somewhat decreases cuttingspeeds, as nitrogen increases the hardness. The addition of boronto'steels congen steels, I submit the following:

Mn s N 3 Percent Percent Percent Percent Percent (l) 0.18 0.60 0.0290.01 0. 007 (2) l5 80 041 000 007 I have found suitable combinations ofsulphur,

nitrogen and boron to give excellent efiects, giving steels capable ofbeing machined at high speed and producing products with excellentfinish. As specific examples of these combinations of sulphur, nitrogenand boron, I submit the followin analyses:

c Mn 0 s N B Percent Percent Percent Percent Percent (l) 0. l8 0. 780.148 0. 009 0. 01 (2) .15 1.03 .216 .011 .007

I have also found that effective steels for machining purposes may beproduced by using phosphorus over the normal amount in conjunction withboron. In steels of this sort I prefer to use boron between 0.004% and0.02%, and phosphorus between 0.035% and 0.12%. As a specific example Igive the following analysis:

0 Mn S P 13 Percent Percent Percent Percent Percent 2,sas,214

In my steels the carbon content will vary from low carbon up to 0.50%,ordinarily running between 0.10% and 0.50%.

Normally, with my steels. the manganese will run from 0.4% to 1.60%,although higher or less manganese contents may be used. Ordinarily it iswell to have a substantial content of manganese as'this element tends toovercome hot shortness. I have employed manganese as high as 2.5%without any disadvantageous counteractin effects upon the boron.

Boron may be used to contribute advantageous effects, recited above, insteels containing up to 16% chromium and I have found that it may beused in steels containing varying amounts of nickel, say up to 3%, orpossibly higher. I have found that the boron addition contributes itsuseful efiects in nitrogen-chromium combinations including theaustenitic varieties of these steels.

In preparing my steels, containing boron, the boron is added in an alloyform either to the steel in the ladle or to the mold. I usually employferro-boron containing 10-20% of elemental boron. I have found thatadding the ferro-boron to the mold is somewhat more economical thanadding it to the ladle. When adding to the ladle it is usually necessaryto employ somewhat more ferroboron than when adding it to the mold, toget the same boron content in the finished product.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patentis:

1. A free-machining steel containing carbon from 0.10% to 0.50%; sulphurfrom 0.06% to 0.30%; boron from 0.004% to 0.02% and the balancesubstantially all iron.

2. A free-machining steel containing carbon from 0.10% to 0.50%; sulphurfrom 0.06% to 0.30%; boron from 0.004% to 0.01% and the balancesubstantially all iron.

DONALD WILLIAM MURPHY.

